Please review the Localization page in the Plugin Handbook. You need to compile a .mo file using msgfmt with your .po file as input. The .mo file must be correctly named and located in the proper location within the WP directory structure. All plugin .mo files are stored in the same place. The .pot and .po files are only a means to an end. WP does not directly use these, only the .mo file is used.

I’m not sure how important the first part of .po files are, but if you look at the .po files of other repository plugins, you’ll see they all have a number of standard meta data entries following msgid ""{ \n }msgstr "". This data will appear in the final .mo file as well. Even if it’s not required, you should provide the information anyway.